I'd check out the examples first. Have you decided which platform you want to use for client development?
Client libs and example projects are linked from here:
Posts made by mobyjames
RE: How to communicate client(iOS/Android) with Nodejs server
posted in Questions & Help •
RE: Joining specific rooms, playing against friends
posted in Questions & Help •
FYI, latest API supports this now. Simply pass the room handle or roomId.
https://docs.colyseus.io/client/client/#join-roomnameorid-string-options-any